6. Riots, routs, and unlawful assemblies must have three persons
at least to constitute them. An unlawful assembly is
when three, or more, do assemble themselves together to
do an unlawful act, as to pull down inclosures, to destroy
a warren or the game therein; and part without doing it,
or making any motion towards it. A rout is where three or
more meet to do an unlawful act upon a common quarrel,
as forcibly breaking down fences upon a right claimed of
common, or of way; and make some advances towards it.
A riot is where three or more actually do an unlawful act
of violence, either with or without a common cause or
quarrel: as if they beat a man; or hunt and kill game in
another's park, chase, warren, or liberty; or do any other
unlawful act with force and violence; or even do a lawful
act, as removing a nusance, in a violent and tumultuous
manner. The punishment of unlawful assemblies, if to the
number of twelve, we have just now seen may be capital,
according to the circumstances that attend it; but, from the
number of three to eleven, is by fine and imprisonment
only. The same is the case in riots and routs by the common
law; to which the pillory in very enormous cases has
been sometimes superadded. And by the statute 13 Hen.
IV. c. 7. any two justices, together with the sheriff or under-sheriff
of the county, may come with the posse comitatus,
if need be, and suppress any such riot, assembly, or
rout, arrest the rioters, and record upon the spot the nature
and circumstances of the whole transaction; which
record alone shall be a sufficient conviction of the offenders.
In the interpretation of which statute it hath been holden,
that all persons, noblemen and others, except women,
clergymen, persons decrepit, and infants under fifteen,
are bound to attend the justices in suppressing a riot, upon
pain of fine and imprisonment; and that any battery,
wounding, or killing the rioters, that may happen in suppressing
the riot, is justifiable. So that our antient law, previous
to the modern riot act, seems pretty well to have
guarded against any violent breach of the public peace;
especially as any riotous assembly on a public or general
account, as to redress grievances or pull down all inclosures,
and also resisting the king's forces if sent to keep
the peace, may amount to overt acts of high treason, by
levying war against the king.

7. Nearly related to this head of riots is the offence of
tumultuous petitioning; which was carried to an enormous
height in the times preceding the grand rebellion. Wherefore
by statute 13 Car. II. st. 1. c. 5. it is enacted, that not
more than twenty names shall be signed to any petition to
the king or either house of parliament, for any alteration
of matters established by law in church or state; unless the
contents thereof be previously approved, in the country,
by three justices, or the majority of the grand jury at the
assises or quarter sessions; and, in London, by the lord
mayor, aldermen, and common council: and that no petition
shall be delivered by a company of more than ten persons:
on pain in either case of incurring a penalty not exceeding
100 l, and three months imprisonment.

The Founders' Constitution
Volume 5, Amendment I (Petition and Assembly), Document 11http://press-pubs.uchicago.edu/founders/documents/amendI_assemblys11.htmlThe University of Chicago Press

Blackstone, William. Commentaries on the Laws of England: A Facsimile of the First Edition of 1765--1769. Chicago: University of Chicago Press, 1979.